CN107959011B - Hierarchical porous lithium titanate-titanium dioxide composite negative electrode material and preparation method thereof - Google Patents
Hierarchical porous lithium titanate-titanium dioxide composite negative electrode material and preparation method thereof Download PDFInfo
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Abstract
A hierarchical porous lithium titanate-titanium dioxide composite negative electrode material and a preparation method thereof are disclosed, wherein the preparation method comprises the following steps: s1, carrying out thermal reaction on a titanium source and a mixed solution of N, N-dimethylformamide and isopropanol in a hydrothermal reaction kettle to obtain a reaction product A; s2, carrying out suction filtration on the reaction product A, and washing a filter cake to obtain a titanium hydroxide hydrate, wherein the titanium hydroxide hydrate has a hierarchical structure and is in a porous submicron particle ball shape; s3, carrying out thermal reaction on the titanium hydroxide hydrate, the lithium salt aqueous solution and the organic solvent in a hydrothermal reaction kettle to obtain a reaction product B; and S4, carrying out suction filtration on the reaction product B, washing and drying a filter cake, and sintering in the air to obtain the spherical graded porous lithium titanate-titanium dioxide composite particles. The composite negative electrode material prepared by the preparation method has excellent specific capacity and cycle performance, and can be used as a lithium ion battery negative electrode material with high multiplying power and capable of working in a wide temperature range.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a hierarchical porous lithium titanate-titanium dioxide composite negative electrode material and a preparation method thereof.
Background
In recent years, lithium ion secondary batteries have been widely used in portable electronic devices, electric vehicles, and energy storage devices due to their advantages of high voltage, long cycle life, high energy density, and high power density. However, in the background of the era in which this rapid charging technology prevails, various applications also put higher demands on lithium ion batteries — safer, longer cycle life, better rate performance and lower temperature performance. However, the commercial graphite-based negative electrode material cannot meet the application requirements of electric vehicles and high-rate devices due to the intrinsic small diffusion constant of the lithium ion battery. Meanwhile, because the de-intercalation potential of lithium ions in the graphite cathode is close to the oxidation-reduction potential of lithium, lithium dendrites are easy to form, the lithium dendrites penetrate through the diaphragm, the anode and the cathode of the battery are in direct contact short circuit, and the battery is heated and even explodes to cause serious safety problems.
Lithium titanate Li of spinel structure4Ti5O12(LTO) has almost no structural change during charging and discharging and is considered to be a "zero strain" material. The theoretical capacity can reach 175mAh g-1The discharge plateau is 1.55V (vertus Li)+/Li), avoiding the formation of lithium dendrites, with better safety. However, lithium titanate itself has a problem of low electron conductivity, and also, in a low-temperature state (i)<At 0 ℃ C, the performance of lithium titanate is also affected by problems such as increased resistance and increased polarization of the battery. Therefore, if a method for modifying lithium titanate can be found, and the method integrates high cycle stability, high rate performance and excellent low-temperature performance, the method will make an important contribution to solving the problem of application of the lithium ion battery under the conditions of high rate and extreme low temperature.
Disclosure of Invention
The invention aims to provide a hierarchical porous lithium titanate-titanium dioxide composite negative electrode material and a preparation method thereof, which integrate high cycle stability, high rate performance and excellent low-temperature performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a hierarchical porous lithium titanate-titanium dioxide composite negative electrode material comprises the following steps:
s1, carrying out thermal reaction on a titanium source and a mixed solution of N, N-dimethylformamide and isopropanol in a hydrothermal reaction kettle to obtain a reaction product A;
s2, carrying out suction filtration on the reaction product A prepared in the step S1, and washing a filter cake to obtain a titanium hydroxide hydrate, wherein the titanium hydroxide hydrate has a hierarchical structure and is in a porous submicron particle ball shape;
s3, carrying out thermal reaction on the titanium hydroxide hydrate prepared in the step S2, a lithium salt aqueous solution and an organic solvent in a hydrothermal reaction kettle to obtain a reaction product B;
s4, carrying out suction filtration on the reaction product B prepared in the step S3, washing and drying a filter cake, and sintering in the air to obtain the spherical graded porous lithium titanate-titanium dioxide composite particles.
A hierarchical porous lithium titanate-titanium dioxide composite negative electrode material is formed by agglomeration of lithium titanate-titanium dioxide composite nanosheets, is composed of petal-shaped submicron spherical particles, and has a two-phase structure of a cubic crystal phase and a tetragonal phase.
The beneficial effects of the invention include: the preparation method has the advantages of simple and safe process, low equipment requirement, low cost and high yield, and the phase of the prepared product is of a two-phase structure of a cubic phase and a tetragonal phase through X-ray diffraction (XRD) spectrum analysis; the powder has the hierarchical porous sphere appearance, and Transmission Electron Microscope (TEM) photos and Scanning Electron Microscope (SEM) photos show that the size and the appearance of the particles are uniform, the specific surface area is large, the dispersibility is good, and the powder particles have single appearance. As a nano self-assembly structure, the hierarchical porous lithium titanate-titanium dioxide composite negative electrode material well combines a two-dimensional nanosheet structure into a macroscopic three-dimensional structure, so that the material has the advantages of a nano structure and a micron structure, the rate capability and the low-temperature performance of the material are improved, and the material has high cycling stability and can be applied to the field of lithium ion batteries as a negative electrode material.
Drawings
Fig. 1 is a process flow diagram of a preparation method of a hierarchical porous lithium titanate-titanium dioxide composite anode material according to an embodiment of the present invention;
fig. 2 is an X-ray diffraction (XRD) pattern of the hierarchical porous lithium titanate-titanium dioxide composite negative electrode material prepared in the embodiment of the present invention;
fig. 3 is a Scanning Electron Microscope (SEM) image of a graded porous lithium titanate-titanium dioxide composite negative electrode material prepared in an embodiment of the present invention;
fig. 4 is a Transmission Electron Microscope (TEM) image of the graded porous lithium titanate-titanium dioxide composite negative electrode material prepared in the embodiment of the present invention.
Fig. 5 shows the 0.2C cycle performance of the graded porous lithium titanate-titanium dioxide composite negative electrode material prepared in the embodiment of the invention at different temperatures.
Detailed Description
The present invention will be described in further detail with reference to the following detailed description and accompanying drawings. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.
As used herein, "room temperature" means 20 to 30 ℃ and preferably 23 to 25 ℃.
Referring to fig. 1 to fig. 4, the present invention provides a preparation method of a hierarchical porous lithium titanate-titanium dioxide composite negative electrode material, including the following steps:
s1, carrying out thermal reaction on a titanium source and a mixed solution of N, N-dimethylformamide and isopropanol in a hydrothermal reaction kettle to obtain a reaction product A;
s2, carrying out suction filtration on the reaction product A prepared in the step S1, and washing a filter cake to obtain a titanium hydroxide hydrate, wherein the obtained titanium hydroxide hydrate has a hierarchical structure and is in a porous submicron particle ball shape;
s3, carrying out thermal reaction on the titanium hydroxide hydrate prepared in the step S2, a lithium salt aqueous solution and an organic solvent in a hydrothermal reaction kettle to obtain a reaction product B;
s4, carrying out suction filtration on the reaction product B prepared in the step S3, washing and drying a filter cake, and sintering in the air to obtain the spherical graded porous lithium titanate-titanium dioxide composite particles.
Wherein, in some embodiments, in step S1, the volume ratio of N, N-dimethylformamide to isopropanol is 1:1 to 1:10, the molar concentration of titanium ions in the mixed solution is 0.05 to 1.0mol/L, and the thermal reaction in step S1 is: reacting for 10 to 30 hours at the temperature of between 180 and 260 ℃. For example, step S1 may preferably include the steps of:
s11, sequentially adding isopropanol and N, N-dimethylformamide into a reaction bottle under the stirring state, and then adding a titanium source;
s12, pouring the solution prepared in the step S11 into a tetrafluoroethylene tank, placing the tetrafluoroethylene tank into a hydrothermal reaction kettle, reacting for 10-30 h at 180-260 ℃, and naturally cooling the hydrothermal reaction kettle to room temperature after the reaction is finished to obtain a reaction product A.
Wherein, in some embodiments, the titanium source can be at least one of tetrabutyl titanate, tetraethyl titanate, isopropyl titanate, and further preferably tetrabutyl titanate. After steps S1 and S2, the chemical formula of the obtained titanium hydroxide hydrate can be represented as H2Ti2O5·H2O, which is white, has a hierarchical structure, is spherical with porous submicron particles, wherein submicron means a size between 800nm and 1 μm.
In step S2, washing with absolute ethanol may be performed to wash off the organic solvent remaining in the step reaction product a.
In some embodiments, in step S3: the molar concentration of lithium ions in the lithium salt aqueous solution is 0.1-10 mol/L; in the reaction system, the molar ratio of lithium ions to titanium ions is controlled to be 0.80-1.60; the volume ratio of the lithium salt aqueous solution to the organic solvent is 1: 1-1: 10; the pH value of the reaction system is 12-14. For example, step S3 may preferably include the steps of:
s31, under the stirring state, putting the titanium hydroxide hydrate prepared in the step S2 and 0.1-10 mol/L lithium salt aqueous solution into a reaction bottle, controlling the molar ratio of lithium ions to titanium ions to be 0.80-1.60, adding an organic solvent, continuing stirring for 10min, adjusting the pH value of the reaction system to be 12-14, and uniformly mixing;
s32, placing the solution prepared in the step S31 in a hydrothermal reaction kettle, heating to 60-110 ℃, maintaining for 2-20 h, and naturally cooling the hydrothermal reaction kettle to room temperature after the reaction is finished to obtain a reaction product B.
In step S31, the pH of the system may be adjusted with sodium hydroxide, and it is more preferable to adjust the pH of the system to 13. The lithium salt in the lithium salt aqueous solution may be at least one of lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, and lithium acetate.
The organic solvent used in step S3 is used to protect the morphology of the titanium hydroxide hydrate from being damaged, and at least one of methanol and ethanol may be selected.
The washing in step S4 may be performed with deionized water and absolute ethanol, respectively.
In some embodiments, the drying process of step S4 may be performed in an oven at 50-120 ℃ for 2-12 h.
In some embodiments, the operating pressure in the hydrothermal reaction kettle in steps S1 and S3 is ≦ 3 MPa.
In some embodiments, the sintering in step S4 is performed at 300-500 ℃ for 2-5 h.
The invention also provides a hierarchical porous lithium titanate-titanium dioxide composite negative electrode material which is formed by agglomeration (or self-assembly) of lithium titanate-titanium dioxide composite nanosheets, is formed by petal-shaped submicron spherical particles and has a two-phase structure of a cubic phase and a tetragonal phase.
Wherein the chemical formula of the composite anode material can be represented as Li4Ti5O12-TiO2，TiO2Is of anatase type, Li4Ti5O12Is of the spinel type; the ratio of lithium titanate and titanium dioxide in the final product can be adjusted during the preparation process by adjusting the ratio of titanium hydroxide hydrate to lithium source, preferably Li4Ti5O12With TiO2The mass ratio is 4: 1.
In some embodiments, the sub-micron size refers to spherical particles having a size between 800nm and 1000 nm.
In some embodiments, the thickness of the nanoplatelets is between 8-10nm and the pore size distribution between the nanoplatelets is between 2-50 nm.
As can be seen from the XRD chart of fig. 2, the composite anode material of the present invention has a two-phase structure of a cubic phase and a tetragonal phase. As shown in fig. 3 and 4, the composite negative electrode material is submicron spheres formed by self-assembling nano sheets, the nano sheets are in a primary structure, and the formed submicron spheres are in a secondary structure, so that the composite negative electrode material can be called a hierarchical structure, wherein a cubic phase and a tetragonal phase are randomly distributed in the composite negative electrode material, the composite negative electrode material has a shape similar to a petal, no serious agglomeration phenomenon occurs between the submicron spheres, and the composite negative electrode material has good dispersibility and large specific surface area.
In the preparation method of the specific embodiment of the invention, a porous titanium hydroxide hydrate submicron-sized particle sphere precursor is obtained firstly, then a lithium source is added, the proportion of lithium titanate and titanium dioxide in the final product is adjusted by adjusting the proportion between the precursor and the lithium source, and the obtained submicron-sized particle has larger pores and larger nanosheets, and when the nanosheets are used as a negative electrode material of a lithium ion battery, the contact between an electrolyte and the material and the ion transmission in the electrode reaction process are facilitated. As shown in fig. 5, the lithium titanate-titanium dioxide composite negative electrode material prepared by the invention can not only play a role in a normal temperature range, but also play a role in a performance at a very low temperature of-40 ℃, is a lithium ion battery negative electrode material capable of working in a wide low temperature range, and widens the applicable temperature environment of the lithium ion battery negative electrode material.
The invention is further illustrated by the following specific examples.
Example 1
A1, sequentially adding 25mL of isopropanol and 10mL of LN, N-dimethylformamide into a 50mL reaction bottle, then adding 1mL of tetrabutyl titanate, and stirring for 10 min;
a2, placing the solution prepared in the step A1 in a hydrothermal reaction kettle, heating the reaction system to 180 ℃, and maintaining the temperature for 30 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
a3, filtering the product obtained in the step A2 by suction; precipitating, and washing with absolute ethyl alcohol for three times; obtaining a porous titanium hydroxide hydrate submicron particle sphere precursor with a white hierarchical structure;
a4, adding 5mL of deionized water and 30mL of ethanol into a 50mL reaction bottle, and adding 0.125g of the porous titanium hydroxide hydrate submicron particle sphere precursor with the white hierarchical structure prepared in the step A3 under the stirring state; then 0.05g of lithium hydroxide monohydrate is weighed and dissolved in the solution, the solution is continuously stirred for 10min, and then the pH value of the solution is adjusted to 12 by using a sodium hydroxide solution;
a5, placing the solution prepared in the step A4 in a hydrothermal reaction kettle, heating the reaction system to 110 ℃, and maintaining for 2 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
and A6, carrying out suction filtration and precipitation on the product obtained in the step A5, washing the product twice with deionized water and absolute ethyl alcohol in sequence, and drying the product in an oven at 120 ℃ for 2 hours to obtain the graded porous lithium titanate-titanium dioxide submicron-grade particle ball. The result of the analysis of an X-ray diffraction (XRD) spectrum (see figure 2) shows that the phases of the obtained hierarchical porous lithium titanate-titanium dioxide submicron-sized particle spheres are cubic phases and tetragonal phases, and no other impurity peak is seen. The Transmission Electron Microscope (TEM) picture (shown in figure 4) and the Scanning Electron Microscope (SEM) picture (shown in figure 3) show that the size and the shape of the obtained hierarchical porous lithium titanate-titanium dioxide submicron particle spheres have better uniformity.
Example 2
A1, sequentially adding 25mL of isopropanol and 10mL of LN, N-dimethylformamide into a 50mL reaction bottle, then adding 1.2mL of tetrabutyl titanate, and stirring for 10 min;
a2, placing the solution prepared in the step A1 in a hydrothermal reaction kettle, heating the reaction system to 200 ℃, and maintaining the temperature for 24 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
a3, carrying out suction filtration and precipitation on the product obtained in the step A2, and washing the product with absolute ethyl alcohol for three times to obtain a porous titanium hydroxide hydrate submicron particle sphere precursor with a white hierarchical structure;
a4, adding 10mL of deionized water and 25mL of methanol into a 50mL reaction bottle, and adding 0.2g of the porous titanium hydroxide hydrate submicron particle sphere precursor with the white hierarchical structure prepared in the step A3 under the stirring state; then 0.13g of lithium nitrate is weighed and dissolved in the solution, the solution is continuously stirred for 10min, and then the pH value of the solution is adjusted to 14 by using a sodium hydroxide solution;
a5, placing the solution prepared in the step A4 in a hydrothermal reaction kettle, heating the reaction system to 90 ℃, and maintaining the temperature for 8 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
and A6, carrying out suction filtration and precipitation on the product obtained in the step A5, washing the product twice with deionized water and absolute ethyl alcohol in sequence, and drying the product in an oven at 80 ℃ for 10 hours to obtain the graded porous lithium titanate-titanium dioxide submicron-sized particle ball.
Example 3
A1, sequentially adding 30mL of isopropanol and 5mL of LN, N-dimethylformamide into a 50mL reaction bottle, then adding 1.2mL of tetrabutyl titanate, and stirring for 5 min;
a2, placing the solution prepared in the step A1 in a hydrothermal reaction kettle, heating the reaction system to 240 ℃, and maintaining for 14 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
a3, carrying out suction filtration and precipitation on the product obtained in the step A2, and washing the product with absolute ethyl alcohol for three times to obtain a porous titanium hydroxide hydrate submicron particle sphere precursor with a white hierarchical structure;
a4, adding 10mL of deionized water and 25mL of ethanol into a 50mL reaction bottle, and adding 0.25g of the porous titanium hydroxide hydrate submicron particle sphere precursor with the white hierarchical structure prepared in the step A3 under the stirring state; then weighing 0.146g of lithium carbonate, dissolving the lithium carbonate in the solution, continuously stirring for 10min, and then adjusting the pH value of the solution to 13 by using a sodium hydroxide solution;
a5, placing the solution prepared in the step A4 in a hydrothermal reaction kettle, heating the reaction system to 75 ℃, and maintaining for 12 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
and A6, carrying out suction filtration and precipitation on the product obtained in the step A5, washing the product twice with deionized water and absolute ethyl alcohol in sequence, and drying the product in an oven at 80 ℃ for 6 hours to obtain the graded porous lithium titanate-titanium dioxide submicron-grade particle.
Example 4
A1, adding 17.5mL of isopropanol and 17.5mL of N, N-dimethylformamide into a 50mL reaction bottle in sequence, then adding 1mL of tetrabutyl titanate, and stirring for 5 min;
a2, placing the solution prepared in the step A1 in a hydrothermal reaction kettle, heating the reaction system to 260 ℃, and maintaining the temperature for 10 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
a3, carrying out suction filtration and precipitation on the product obtained in the step A2, and washing the product with absolute ethyl alcohol for three times to obtain a porous titanium hydroxide submicron-grade particle ball precursor with a white hierarchical structure;
a4, adding 15mL of deionized water and 15mL of methanol into a 50mL reaction bottle, and adding 0.3g of the porous titanium hydroxide hydrate submicron particle sphere precursor with the white hierarchical structure prepared in the step A3 under the stirring state; then 0.19g of lithium acetate is weighed and dissolved in the solution, the solution is continuously stirred for 10min, and then the pH value of the solution is adjusted to 13.5 by using a sodium hydroxide solution;
a5, placing the solution prepared in the step A4 in a hydrothermal reaction kettle, heating the reaction system to 60 ℃, and maintaining the temperature for 20 hours; after the reaction is finished, naturally cooling the hydrothermal reaction kettle to room temperature;
and A6, carrying out suction filtration and precipitation on the product obtained in the step A5, washing the product twice with deionized water and absolute ethyl alcohol in sequence, and drying the product in an oven at 50 ℃ for 12 hours to obtain the graded porous lithium titanate-titanium dioxide submicron-sized particle ball.
The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and such substitutions and modifications are to be considered as within the scope of the invention.
Claims (7)
1. A preparation method of a hierarchical porous lithium titanate-titanium dioxide composite negative electrode material is characterized in that the hierarchical porous lithium titanate-titanium dioxide composite negative electrode material is formed by self-assembling lithium titanate-titanium dioxide composite nanosheets, is composed of petal-shaped submicron spherical particles and has a two-phase structure of a cubic crystal phase and a tetragonal phase, and comprises the following steps:
s1, carrying out thermal reaction on a titanium source and a mixed solution of N, N-dimethylformamide and isopropanol in a hydrothermal reaction kettle to obtain a reaction product A, wherein the thermal reaction refers to: reacting for 10 to 30 hours at the temperature of between 180 and 260 ℃;
s2, carrying out suction filtration on the reaction product A prepared in the step S1, and washing a filter cake to obtain a titanium hydroxide hydrate, wherein the titanium hydroxide hydrate has a hierarchical structure and is in a porous submicron particle ball shape;
s3, carrying out thermal reaction on the titanium hydroxide hydrate prepared in the step S2, a lithium salt aqueous solution and an organic solvent in a hydrothermal reaction kettle to obtain a reaction product B, wherein the thermal reaction refers to: reacting for 2-20 h at 60-110 ℃, wherein the organic solvent is at least one of ethanol and methanol;
s4, carrying out suction filtration on the reaction product B prepared in the step S3, washing and drying a filter cake, and sintering the filter cake for 2-5 hours at 300-500 ℃ in the air to obtain the spherical graded porous lithium titanate-titanium dioxide composite particles.
2. The method according to claim 1, wherein in step S1, the volume ratio of N, N-dimethylformamide to isopropanol is 1:1 to 1: 10; in the mixed solution, the molar concentration of titanium ions is 0.05-1.0 mol/L.
3. The method of claim 1, wherein in step S3: the molar concentration of lithium ions in the lithium salt aqueous solution is 0.1-10 mol/L; in the reaction system, the molar ratio of lithium ions to titanium ions is controlled to be 0.80-1.60; the volume ratio of the lithium salt aqueous solution to the organic solvent is 1: 1-1: 10; the pH value of the reaction system is 12-14.
4. The method of claim 1, wherein the titanium source is at least one of tetrabutyl titanate, tetraethyl titanate, isopropyl titanate; the lithium salt in the lithium salt aqueous solution is at least one of lithium hydroxide monohydrate, lithium nitrate, lithium carbonate and lithium acetate.
5. A graded porous lithium titanate-titanium dioxide composite negative electrode material prepared by the preparation method of any one of claims 1-4.
6. The hierarchical porous lithium titanate-titanium dioxide composite negative electrode material of claim 5, wherein the sub-micron-sized means that the size of spherical particles is between 800nm and 1000 nm.
7. The hierarchical porous lithium titanate-titanium dioxide composite negative electrode material of claim 5, wherein the thickness of the nanosheets is between 8-10nm, and the pore size distribution between the nanosheets is between 2-50 nm.
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